640723 has 4 divisors (see below), whose sum is σ = 642600. Its totient is φ = 638848.

The previous prime is 640691. The next prime is 640727. The reversal of 640723 is 327046.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 640723 - 2⁵ = 640691 is a prime.

It is an Ulam number.

It is a Duffinian number.

640723 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 640694 and 640703.

It is not an unprimeable number, because it can be changed into a prime (640727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 265 + ... + 1162.

It is an arithmetic number, because the mean of its divisors is an integer number (160650).

2⁶⁴⁰⁷²³ is an apocalyptic number.

640723 is a deficient number, since it is larger than the sum of its proper divisors (1877).

640723 is a wasteful number, since it uses less digits than its factorization.

640723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1876.

The product of its (nonzero) digits is 1008, while the sum is 22.

The square root of 640723 is about 800.4517474526. The cubic root of 640723 is about 86.2098265616.

Adding to 640723 its reverse (327046), we get a palindrome (967769).

The spelling of 640723 in words is "six hundred forty thousand, seven hundred twenty-three".